CN114759949A - Fast code capture method in BPSK modulation direct sequence spread spectrum communication - Google Patents
Fast code capture method in BPSK modulation direct sequence spread spectrum communication Download PDFInfo
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Abstract
The invention relates to the field of wireless communication equipment, in particular to a fast code capturing method in BPSK modulation direct sequence spread spectrum communication. The invention can reduce the capture time, has no relation between the capture time and the distance uncertainty, improves the code capture efficiency, completes the main operation through the most commonly used FIR filter in the digital signal processing, and is easy to realize.
Description
Technical Field
The invention relates to the field of wireless communication equipment, in particular to a fast code capturing method in BPSK modulation direct sequence spread spectrum communication.
Background
Code acquisition (PN) is an important technique in spread spectrum communications, and is to align the PN code of a local receiver with the received PN code within one chip (T second period), and complete synchronization after symbol acquisition has been achieved and code loop acquisition enters steady-state tracking.
When designing a pseudo code acquisition system of a spread spectrum receiver, a plurality of parameters need to be considered, the uncertainty of frequency and time is two most important parameters of acquisition performance, and the uncertainty of time comprises two aspects, namely the actual uncertainty of a transmitting clock and a receiving clock, and the uncertainty of distance. The larger the effective time uncertainty is, the longer the time required for completing the acquisition, and for a general slow acquisition method, the influence of noise is not considered, if the length of the PN code is L, the duration of one chip is T, the acquisition can be determined as long as one time of "hit", the acquisition time is related to the distance uncertainty, the longest acquisition time is L T, the occurrence probability of the longest acquisition time is 1/L, and if the influence of noise is considered, M times of "hits" must be continuously determined as acquisition to reduce the false acquisition false probability, and the longest acquisition time is M L T.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a quick code acquisition method in BPSK modulation direct sequence spread spectrum communication, which reduces the acquisition time, has no relation with the uncertainty of the distance and improves the code acquisition efficiency.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme.
A fast code capture method in BPSK modulation direct sequence spread spectrum communication comprises the following steps:
step 1, receiving signals and local carrier signals cos (omega) generated by local carrier NCO respectively1t+θ1) And a Q local carrier signal sin (omega) generated by a local carrier NCO1t+θ1) Multiplying and mixing to obtain signals I0Sum signal Q0；
Step 2, signal I0Sum signal Q0Respectively low-pass filtering to obtain baseband signals I1And baseband signal Q1；
Step 3, for baseband signal I1And baseband signal Q1Filtering and extracting respectively, extracting two samples in each chip duration to obtain low-sampling signals I2And low sampling signal Q2；
Step 4, low sampling signal I2And low sampling signal Q2Respectively input into FIR filters to respectively obtain data I3And data Q3；
Step 5, data I is processed3And data Q3For each pair of samples, squaring and re-squaring, and taking frequency difference into account to obtain R 0,R1,R2.....RiI-0, 1., 2L-1; let R bexIs R0,R1,R2.....RiX is a serial number;
step 6, setting the maximum value RxComparing with a capture threshold eta, and sending an indication signal to a code generator according to a comparison result;
and 7, outputting a spread spectrum sequence by the code generator according to the indication signal.
Compared with the prior art, the invention has the beneficial effects that: if the noise influence is not considered, code capture can be realized within one code element time L & ltTc & gt, if the noise influence is considered, the longest capture time is M & ltTc & gt, and the longest capture time is only 1/L of the longest capture time of the ordinary slow capture, so that the capture time is reduced; the capturing time is irrelevant to the uncertainty of the distance, so that the code capturing efficiency is improved; the main operation is completed by the most commonly used FIR filter in digital signal processing, which is easy to realize.
Drawings
The invention is described in further detail below with reference to the figures and specific embodiments.
Fig. 1 is a flowchart of a fast code acquisition method for BPSK modulated direct sequence spread spectrum communication according to the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, a method for fast code acquisition in BPSK modulated direct sequence spread spectrum communication includes the following steps:
step 1, receiving signals and local carrier signals cos (omega) generated by local carrier NCO respectively1t+θ1) And a Q local carrier signal sin (omega) generated by a local carrier NCO1t+θ1) Multiplying and mixing to obtain signals I0Sum signal Q0；
Specifically, for BPSK chip (PN code) modulation, the complex envelope form is as follows:
wherein, P is the power of the spread spectrum signal; pT(T) is a unit pulse of T seconds, starting at T-0 and ending at T-T seconds; k is an integer representing the time of how many T the unit pulse is delayed, T is the unit pulse duration, i.e. the pulse width; a iskCoefficients of a chip sequence of a direct spreading sequence, ak∈{1，-1}；
For ease of discussion, the chip sequence is usually represented by PN (t), then
In addition, the data sequence d (t) is defined as
Wherein, PMT(t) is a unit pulse of duration MT, PMTJ in (T-jMT) is an integer representing how many MT times a unit pulse is delayed, M represents exactly M chips per bit or code bit, and T is a unit pulse PT(t) width; djThe value is 1 or-1 for discrete data symbols; each bit djThe probability of taking 1 or-1 is 1/2, and each d jAre all statistically independent from each other;
when BPSK chip modulation uses BPSK data modulation, the complex envelope form can be abbreviated as:
and carrying out carrier modulation on the signal v (t) to obtain a spread spectrum signal in the form of:
wherein, PtFor spreading frequencyThe signal power;
the signal modulated by the carrier generates attenuation and phase delay in the transmission process, so the received signal y (t) can be written as:
where P is the power of the received signal and P < Pt，TpFor signal delay, carrier phase θ0Simulating by using a uniform random variable, wherein the distribution area is 0-2 pi radian, n (t) is noise, and J (t) is an interference signal;
signal I0Comprises the following steps:
signal Q0Comprises the following steps:
step 2, signal I0Sum signal Q0Respectively low-pass filtering to obtain baseband signals I1And baseband signal Q1；
In particular, the baseband signal I1Comprises the following steps:
baseband signal Q1Comprises the following steps:
step 3, for baseband signal I1And baseband signal Q1Filtering and extracting respectively, extracting two samples in each chip duration to obtain low-sampling signals I2And low sampling signal Q2；
Step 4, low sampling signal I2And low sampling signal Q2Respectively input into FIR filters to respectively obtain data I3And data Q3；
Specifically, the FIR filter coefficient takes the value of 2 times of the sampling value of the spreading code sequence pn (t); the length of the spreading code sequence PN (t) is L, and the coefficient length of the FIR filter is 2L;
Data I3Comprises the following steps:
data Q3Comprises the following steps:
wherein i is 0,1, 2L-1, TbDelaying the spreading code sequence, TpThe signal is delayed.
Step 5, data I is processed3And data Q3For each pair of samples, squaring and re-squaring, and taking frequency difference into account to obtain R0,R1,R2.....RiI-0, 1, ·, 2L-1; let RxIs R0,R1,R2.....RiX is a serial number;
in particular, the method comprises the following steps of,
when T isbAnd TpDiffering by less than half a chip period (i.e. one half chip period)
) Due to the autocorrelation of the spreading code, RiAnd max.
Step 6, mixing the obtained mixtureLarge value of RxComparing with a capture threshold eta, and sending an indication signal to a code generator according to a comparison result;
in particular, if the maximum value R isxIf the value is greater than eta, judging whether the capture is finished; if the capture is not finished, a capture indication signal and a serial number x are output to a code generator; if the capture is finished, outputting a serial number 0 to a code generator;
if the maximum value RxIf not, judging whether the capture is finished; if the capture is not finished, the serial number x is made to be 0 and output to the code generator; if the capture is finished, judging whether the maximum value R is continuously carried out for 3 timesxIf not, outputting a capture losing indication signal to the code generator, otherwise, outputting a serial number 0 to the code generator.
Step 7, the code generator outputs spread spectrum sequence sampling points according to the indication signal;
Specifically, if the code generator receives the missed-capture indication signal, the code generator resets, and the code generator resets from the 0 th sampling point a0Starting to output the sample point of the spread code sequence again, and outputting the spread code sequence when Ta is Tb
2 times the number of sampling points, i.e. a spreading code sequence a with 2L output sampling points0,a0,a1,a1,a2,a2.....aL-1,aL-1Wherein T isaThe output time of the 0 th sampling point of the code generator; resetting the FIR filter simultaneously and returning to the step 4;
if the code generator only receives the serial number 0, the code generator does not reset and delay, and normally outputs the spread spectrum code sequence
2 times the number of sampling points, i.e. a spreading code sequence a with 2L output sampling points0,a0,a1,a1,a2,a2.....aL-1,aL-1，；
If the code generator receives the capture indication signal and the serial number x, the code generator headResetting is performed first, and then delaying by x samples (i.e., delaying
After the time) of (d), at this time
Outputting spread spectrum code sequences
2 times the number of sampling points, i.e. a spreading code sequence a with 2L output sampling points0,a0,a1,a1,a2,a2.....aL-1,aL-1When the phase difference between the spread spectrum code sequence output by the code generator and the pseudo random code of the received signal is less than half a chip period
The capture is completed.
Although the present invention has been described in detail in this specification with reference to specific embodiments and illustrative embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made thereto based on the present invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (7)
1. A fast code acquisition method in BPSK modulated direct sequence spread spectrum communication, comprising the steps of:
step 1, receiving signals and local carrier signals cos (omega) generated by local carrier NCO respectively1t+θ1) And a Q-path local carrier signal sin (omega) generated by a local carrier NCO1t+θ1) Multiplying and mixing to obtain signals I0Sum signal Q0；
Step 2, signal I0Sum signal Q0Respectively low-pass filtering to obtain baseband signals I1And baseband signal Q1；
Step 3, for baseband signal I1And baseband signal Q1Filtering and extracting respectively, extracting two samples in each chip duration to obtain low-sampling signals I2And low sampling signal Q2；
Step 4, low sampling signal I2And low sampling signal Q2Respectively input into FIR filters to respectively obtain data I3And data Q3；
Step 5, data I is processed3And data Q3For each pair of samples, squaring and re-squaring, and taking frequency difference into account to obtain R0,R1,R2.....RiI-0, 1, ·, 2L-1; let RxIs R0,R1,R2.....RiX is a serial number;
step 6, setting the maximum value RxComparing with a capture threshold eta, and sending an indication signal to a code generator according to a comparison result;
and 7, outputting a spread spectrum sequence by the code generator according to the indication signal.
2. The method of claim 1, wherein in step 1, the received signal is:
Wherein P is the power of the received signal; pn (t) represents a chip sequence; d (t) represents a data sequence; t ispDelaying the signal; theta0The carrier phase is distributed in a uniform random variable with 0-2 pi radian; n (t) is noise; j (t) is an interference signal;
signal I0Comprises the following steps:
signal Q0Comprises the following steps:
3. the method of claim 1, wherein in step 2, the baseband signal I is used as the fast code acquisition in BPSK modulated direct sequence spread spectrum communications1Comprises the following steps:
baseband signal Q1Comprises the following steps:
4. the method of claim 1, wherein in step 4, the FIR filter coefficients are 2 times the sample values of the spreading code sequence pn (t); the length of the spreading code sequence PN (t) is L, and the coefficient length of the FIR filter is 2L;
data I3Comprises the following steps:
data Q3Comprises the following steps:
wherein i is 0,1, 2L-1, TbDelaying the spreading code sequence, TpThe signal is delayed.
5. The method of claim 1A fast code acquisition method in BPSK modulation direct sequence spread spectrum communication, characterized in that in step 5, RiThe calculation method is as follows:
wherein, i is 0,1, 2L-1.
6. The method of claim 1, wherein step 6 is performed specifically if the maximum value R is R xIf the current is greater than eta, judging whether the capture is finished; if the capture is not completed, a capture indication signal and a serial number x are output to a code generator; if the capture is finished, outputting a serial number 0 to a code generator;
if the maximum value RxIf the current value is not greater than eta, judging whether the capture is finished or not; if the capture is not completed, the serial number x is made to be 0 and output to the code generator; if the capture is finished, judging whether the maximum value R is continuously carried out for 3 timesxIf not, outputting a capture losing indication signal to the code generator, otherwise, outputting a serial number 0 to the code generator.
7. The method of claim 1, wherein the code generator is reset if the code generator receives the mis-acquisition indication signal, and the code generator resets from the 0 th sampling point a0Starting to re-output an output spread code sequence
2 times the number of sampling points, i.e. a spreading code sequence a with 2L output sampling points0,a0,a1,a1,a2,a2.....aL-1,aL-1(ii) a Resetting the FIR filter simultaneously and returning to the step 4;
if the code generator only receives the serial number 0, the code generator normally outputs the spreading code sequence
2 times the number of sampling points, i.e. a spreading code sequence a with 2L output sampling points0,a0,a1,a1,a2,a2.....aL-1,aL-1，；
If the code generator receives the capture indication signal and the serial number x, the code generator is first reset and then delayed 
After time of (3), outputting the spread spectrum code sequence
2 times of sampling points, i.e. spreading code sequence a with 2L output samples0,a0,a1,a1,a2,a2.....aL-1,aL-1And completing the capture.
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| CN113595586A (en) * | 2021-06-02 | 2021-11-02 | 西安电子科技大学 | Direct sequence spread spectrum signal capturing and tracking method based on MD-PMF-FFT |
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| US5640416A (en) * | 1995-06-07 | 1997-06-17 | Comsat Corporation | Digital downconverter/despreader for direct sequence spread spectrum communications system |
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